Blade pitch adjustment device

ABSTRACT

A blade pitch adjustment system may adjust the pitch of a plurality of blades. A height adjustment assembly adjusts a distance between a rotatable blade assembly and a thrust collar. Adjusting the distance between the assembly and the collar changes the pitch of the blades of the machine. Two or more blade pitch adjustment systems may be adjusted at the same time, at the same rate. For concurrent adjustment, systems are connected to a rotating member by tension cables. A linear actuator rotates the rotating member, changing the tension on the tension cables, actuating the systems to change the pitch of the blade assemblies. The pitch of the blade assemblies may have an offset or bias which may be adjusted for with a sliding member, which may be powered by a linear actuator. The system may be used with a concrete finishing machine.

RELATED APPLICATIONS

The present disclosure claims benefit of U.S. Provisional Patent Application No., 61/138,200, filed on Dec. 17, 2008, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

Concrete finishing machines have been used for many years to level and finish large concrete pads. Such machines typically include a rotatable trowel blade assembly having a plurality (e.g., three, four, five, six, etc.) of generally planar trowel blades mounted on trowel arms projecting radially outwardly from a common hub, all of which are rotated by a power unit, such as a gasoline engine. The trowel blades rest directly on the concrete surface to be finished and support the machine's entire weight.

Concrete finishing machines typically further include a mechanism that may controllably rotate the trowel blades about their respective radial axes (“blade pitch adjustment mechanism”), to change their pitch relative to the concrete surface to be finished. Changing the pitch of the blades correspondingly changes the proportion of blade surface contacting the concrete surface, such that the machine's weight is supported by a larger or smaller area of the surface.

In use, a concrete finishing machine makes several passes over the concrete surface as the concrete hardens, with the blade pitch being specially selected for each pass. In the initial pass, when the concrete is still very wet and plastic, the blade pitch is usually adjusted to be substantially parallel with the concrete surface, thereby lying flat upon it and spreading the machine's weight over a maximum surface area. In subsequent passes, as the concrete hardens and becomes less plastic, the blade pitch is progressively increased, with the pitch used in the final pass sometimes being as much as about 30 degrees.

Past concrete finishing machines have had blade pitch adjustment mechanisms that can adjust the pitch of the trowel blades. Typically, the pitch of the trowel blades is adjusted by applying a force to a lever that is operatively connected to each of the trowel blades. The adjustment has previously been done by a user with a handle connected to a tension cable, further connected to a fork and collar system. Typically, the fork is pivotally attached to the frame of the concrete finishing machine and is connected to the tension cable. When the tension of the cable is adjusted, the fork pivots with respect to the frame of the machine, moving the tines of the fork up or down in an arc. The tines apply pressure to the collar, moving it to a lower or higher position. The levers of the trowel blades contact the collar and rotate the trowel blades with the position of the collar, changing the pitch of the blades with respect to the concrete surface.

Because the fork is pivotally attached to the frame of the machine, the fork tines move in an arc as they are adjusted. The movement of the tines in an arc creates a frictional path across the surface of the collar, causing wear to the fork and the collar in the contact areas. Typically, the fork has two tines, which contact the collar at one point each. The two points of contact form a line about which the collar pivots, applying a tilting force to the collar at many positions. The tilting force may cause uneven wear to the collar, the fork, and to other components of the machine, and may shift the balance of the machine, or affect the control of the machine.

Additionally, the finish of the concrete surface may be affected by the tilting force, as applied to the collar, and thus the rotating blade assembly. If the rotating blade assembly is substantially tilted while the concrete finishing machine is finishing concrete, each blade will effectively have a different pitch angle; the pitch angle of each blade changing as the rotating blade assembly rotates. Instead of being maintained in the same plane, the trailing edges of the blades of a tilted rotating blade assembly may follow the rough contour of the concrete, thus allowing bumps and troughs to remain in the concrete surface.

Prior concrete finishing machines with multiple rotatable blade assemblies have had blade pitch adjustment mechanisms that are manually actuated with linkages or tension cables, or alternatively, power adjusted with a hydraulic cylinder. Manual actuation mechanical pitch adjustment systems are reliable and generally need less adjustment than power actuators. However, manual actuation pitch adjustment systems are generally large and bulky and require that linkages or tension cables be configured such that they can be adjusted by the strength of the user alone.

Power actuated pitch adjustment systems are easier to use, but generally require at least one hydraulic cylinder per blade pitch adjustment mechanism. Often hydraulic cylinders leak fluid, which may cause hydraulic cylinders to move or drift over time. Hydraulic cylinders may leak at different rates, which may be problematic when using a matched set of hydraulic cylinders for a matched function. For example, a plurality of hydraulic cylinders that have actuated a plurality of blade pitch adjustment mechanisms, will drift over time at different rates with respect to each other, due to the fluid leakage. This mismatched drift will result in a mismatched blade pitch between a plurality of blade assemblies over time, which may necessitate a manual adjustment of the hydraulic cylinders.

SUMMARY

An embodiment of a blade pitch adjustment system is disclosed, which may comprise a thrust collar, a rotatable blade assembly coaxial with and persistently contacting the thrust collar, with the rotatable blade assembly being operatively parallel to the thrust collar. The blade pitch adjustment system may further comprise a plurality of blades that are configured to have an adjustable pitch and a height adjustment assembly configured to be coaxial with the thrust collar and the rotatable blade assembly and configured to change a distance between the thrust collar and the rotatable blade assembly such that the thrust collar and the rotatable blade assembly remain operatively parallel to each other before, during, and after a change in distance. Changing the distance between the thrust collar and the rotatable blade assembly may adjust the pitch of the blades.

The height adjustment assembly may be operatively connected to the thrust collar and may be configured to adjust the position of the thrust collar with respect to the rotatable blade assembly while keeping the thrust collar operatively parallel to the rotatable blade assembly. The height adjustment assembly may be operatively connected to the rotatable blade assembly and may be configured to adjust the position of the rotatable blade assembly up and down with respect to the thrust collar while keeping the rotatable blade assembly operatively parallel to the thrust collar. The blade pitch adjustment system may further comprise a power unit mated with a power transfer shaft. The power transfer may be connected to the rotatable blade assembly. The rotatable blade assembly may further comprise a hub connecting to a plurality of rotatable blade arms. Each of the rotatable blade arms may comprise at least one lever. One or more of the plurality of blades may be attached to each rotatable blade arm. The lever may be configured to persistently contact at least a portion of the thrust collar. The height adjustment assembly may comprise an outer ring, a profile follower, a bearing that may be positioned coaxially with the outer ring, and a height adjustment collar. The height adjustment collar may comprise one or more height adjustment profiles. The profile follower may be configured to contact and travel along the height adjustment profiles. The profile follower may comprise a plurality of cams, a plurality of bearings, or a plurality of complementary ramps.

Another embodiment of a blade pitch adjustment system is disclosed, which may comprise a thrust collar and a rotatable blade assembly operatively connected to and operatively parallel with the thrust collar. The rotatable blade assembly may comprise a plurality of blades that are configured to have an adjustable pitch. The blade pitch adjustment system may further comprise a height adjustment assembly, which may comprise at least three contact points, which may operatively form a movable plane, and may be configured to adjust a distance between the thrust collar and the rotatable blade assembly. The distance may be adjusted by adjusting the height of the at least three contact points. The thrust collar and the rotatable blade assembly may remain operatively parallel to each other during and after distance adjustment. Adjusting the distance between the thrust collar and the rotatable blade assembly may correspondingly adjust the pitch of the blades. The three contact points may operatively connect to the thrust collar and may be configured to adjust the position of the thrust collar with respect to the rotatable blade assembly while keeping the thrust collar operatively parallel to the rotatable blade assembly. The at least three contact points may operatively connect to the rotatable blade assembly and may be configured to adjust the position of the rotatable blade assembly with respect to the thrust collar while keeping the rotatable blade assembly operatively parallel to the thrust collar. The rotatable blade assembly, the thrust collar, and the three contact points may be coaxial. The height adjustment assembly may comprise an outer ring and a bearing operatively connected to the outer ring and positioned coaxially within the outer ring.

An embodiment of a concrete finishing machine is disclosed, which may comprise a frame, a guard connected to the frame, a power unit connected to the frame, and a rotatable blade assembly operatively connected to the power unit. The rotatable blade assembly may comprise a plurality of blades that are configured to have an adjustable pitch. The plurality of blades may be rotatably connected to a hub. The rotatable blade assembly may be generally planar. The concrete finishing machine may further comprise a thrust collar, which may comprise a planar rim and may be configured to contact at least a portion of the rotatable blade assembly at the planar rim. The planar rim may be operatively parallel to the plane of the rotatable blade assembly. The concrete finishing machine may further comprise a height adjustment assembly that may be configured to adjust a distance between the thrust collar and the rotatable blade assembly. The planar rim of the thrust collar and the plane of the rotatable blade assembly may remain operatively parallel to each other during and after distance adjustment.

The concrete finishing machine may further comprise an actuator configured to actuate the height adjustment assembly. The concrete finishing machine may further comprise a plurality of rotatable blade assemblies, a plurality of height adjustment assemblies, and a plurality of thrust collars. The distance between the guard and the concrete surface may be substantially the same, regardless of the pitch of the plurality of blades. The concrete finishing machine may further comprise a power transfer shaft operatively connected to the power unit. The power transfer shaft may operatively connect the rotatable blade assembly to the height adjustment assembly.

The concrete finishing machine may further comprise a frame member operatively connected to the frame, and a tension adjustment member that may be connected to the frame member at a connecting point. The tension adjustment member may have a plurality of ends. The concrete finishing machine may further comprise a plurality of tension cables operatively connected to the plurality of ends of the tension adjustment member and a first actuator that may comprise a first end that may be connected to the tension adjustment member and may comprise a second end that may be connected to the frame member. The blade pitch adjustment system may further comprise a mounting member connected to the frame. The frame member may be slidably connected to the mounting member. The blade pitch adjustment system may further comprise a second actuator. The second actuator may comprise a first end and may comprise a second end. The first end of the second actuator may be connected to the mounting member. The second end of the second actuator may be operatively connected to the tension adjustment member.

These and other embodiments of the present application will be discussed more fully in the description. The features, functions, and advantages can be achieved independently in various embodiments of the claimed invention, or may be combined in yet other embodiments.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a partially exploded perspective view of an embodiment of a blade pitch adjustment system of a concrete finishing machine;

FIG. 2 is a cut-away side view of the blade pitch adjustment system of FIG. 1;

FIG. 3A is a perspective view of the blade pitch adjustment system of FIG. 1 with a small blade pitch;

FIG. 3B is a perspective view of a blade pitch adjustment system of FIG. 1 with a larger blade pitch;

FIG. 4 is a block diagram of another embodiment of a blade pitch adjustment system;

FIG. 5 is a block diagram of another embodiment of a blade pitch adjustment system;

FIG. 6 is a perspective view of a ride-on style concrete finishing machine with an embodiment of a blade pitch adjustment system;

FIG. 7 is a perspective view of a prior art walk-behind style concrete finishing machine;

FIG. 8 is a front view of an embodiment of a blade pitch adjustment actuation system;

FIG. 9 is front view of an embodiment of a bias adjustment actuation system;

FIG. 10 is a perspective view of a ride-on style concrete finishing machine with the top removed and comprising an embodiment of a blade pitch adjustment actuation system;

FIG. 11 is a partially exploded perspective view of the ride-on style concrete finishing machine of FIG. 10 with the top removed and showing the embodiment of a blade pitch adjustment actuation system;

FIG. 12A is a perspective view of another embodiment of a blade pitch adjustment actuation system;

FIG. 12B is an exploded perspective view of the embodiment illustrated in FIG. 12A.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that modifications to the various disclosed embodiments may be made, and other embodiments may be utilized, without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.

The present application describes a blade pitch adjustment system located on a machine. Although this mechanism is described primarily with reference to adjusting the trowel blade pitch of a concrete finishing machine, those of ordinary skill in the art will appreciate that the blade pitch adjustment system can be used to perform numerous other functions in connection with a wide variety of machines. For example, in some embodiments, the blade pitch adjustment system can be used to control the blade pitch of a fan or to control the pitch of blades associated with other suitable machines.

FIGS. 1 and 2 show a partially exploded perspective view and a cut-away side view, respectively, of an embodiment of a blade pitch adjustment system 100. In the illustrated embodiment, the blade pitch adjustment system 100 comprises a rotatable blade assembly 102, a power transfer shaft 120, a thrust collar 115 having a lower rim 118, a gearbox 140, and a height adjustment assembly 160.

The gearbox 140 comprises a housing 141, a power unit input 145, a hub 142, and a projection 144 (shown in FIG. 2). The hub 142 may be located at approximately the center of the gearbox 140 and may extend from the top to the bottom of the housing 141. The hub 142 is configured to mate with the power transfer shaft 120, may be splined, and may be operatively connected to a power unit (not shown). As shown in FIG. 1, the height adjustment assembly 160 connects to the top of the housing 141 and the thrust collar 115 connects to the bottom of the housing 141.

The power unit input 145 of the gearbox 140 is configured to operatively connect to a power unit (not shown), such as an internal combustion engine, a pneumatic power unit, a hydraulic motor, an electric motor, or another suitable power unit, as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure. Some power units may preclude the use of the gearbox 140, such as, for example, by having the power unit directly connected to the power transfer shaft 120.

In some embodiments, the power transfer shaft 120 may be splined. As shown in FIG. 2, one end of the shaft 120 may be connected to the height adjustment assembly 160 by a retainer ring 122 that may be removably fitted into a complementary profile or groove formed in the shaft 120. The other end of the shaft 120 may be rigidly connected to the rotatable blade assembly 102 by a connector, such as a retainer ring, a bolt, or another suitable connector.

The rotatable blade assembly 102 comprises a common hub 110, which has a plurality of connecting ports 103 radiating out from the center, and is connected to the power transfer shaft 120. A rotatable blade arm 104 may be rotatably connected to each of the connecting ports 103. A blade 105 and a lever 106 may be rigidly connected to each rotatable blade arm 104. Each rotatable blade arm 104 is further connected to a guide 109, such as a bushing, journal bearing, or roller bearing, which is connected to a support ring 108. A bias spring 101 may be positioned coaxially about the connecting port 103 and may be configured to contact the lever 106 such that the rotatable blade arm 104 is biased to rotate about its axis. The lever 106 is configured to contact the lower rim 118 of the thrust collar 115, which opposes rotation of the lever 106 past the rim 118. The angle at which the lever 106 contacts the rim 118 may be adjusted by changing the length of the lever 106. Additionally, the angle at which the lever 106 contacts the rim 118 may be fine-tuned by an adjustment mechanism (not shown), such as a bolt that may be adjustably connected at an end of the lever 106

The thrust collar 115 comprises an outer collar 116 that includes the lower rim 118 and a bearing 117, such as a bushing, journal bearing, roller bearing, or other suitable bearing, as would be apparent to one of ordinary skill in the art given the benefit of this disclosure. In the embodiment illustrated by FIG. 1, the bearing 117 of thrust collar 115 is mated to the projection 144 of the gearbox 140, such that the outer collar 116 may rotate freely with respect to the gearbox 140.

As illustrated in FIG. 1, the height adjustment assembly 160 comprises an outer ring 162 and a bearing 164, such as a bushing, journal bearing, or thrust bearing, located coaxially within the outer ring 162. The height adjustment assembly further comprises a height adjustment lever 165 connected to and projecting from a side of the outer ring 162, a plurality of cams 163 connected to the outside of the outer ring 162, and a height adjustment collar 166. The height adjustment collar 166 is attached to the gearbox 140 in the embodiment illustrated by FIG. 1. The bearing 164 may be splined and may be connected to the shaft 120 by the retainer ring 122.

As shown in FIG. 1, the collar 166 comprises a plurality of height adjustment profiles 161, such as ramps or inclines, that may be substantially similar and equally spaced. As shown in FIG. 1, the plurality of cams 163 is configured to follow the profiles 161 of the collar 166. The cams 163 may be rotatably connected to the outer ring 162, such that friction is reduced when the cams 163 follow the contours of the profiles 161. In alternative embodiments, the outer ring 162 may be configured with other profile following systems, such as bearings, bushings, complementary ramps, or other suitable profile followers. In other embodiments, the height adjustment assembly 160 may comprise a single, actuated, substantially planar, annular ring that may contact a bottom surface of the outer ring 162.

The height adjustment lever 165 may be further connected to a user actuated adjustment mechanism, such as a linear actuator, linkage, and/or tension cable. The lever 165 may be actuated to move the outer ring 162 about the axis of the shaft 120. Rotation of the outer ring 162 will cause the cams 163 to follow the profiles 161 of the height adjustment collar 166, which may raise or lower the outer ring 162 with respect to the gearbox 140 and the thrust collar 115. As shown in FIG. 1, the shaft 120 and rotatable blade assembly 102 are connected to the outer ring 162 by retainer ring 122 and will raise or lower with the outer ring 162.

To adjust the pitch of the blades 105, such as, for example, to be more parallel, or have a smaller pitch, with respect to a concrete surface 130, the outer ring 162 of the height adjustment assembly 160 may be turned such that the distance between the outer collar 162 and the gearbox housing 141 and thrust collar 115 is reduced. The cams 163 will follow the contours of the profiles 161, increasing the distance between the rotatable blade assembly 102 and the rim 118 of the thrust collar 115. Greater space between the rotatable blade assembly 102 and the rim 118 allows the levers 106 and arms 104 to rotate, bringing the blades 105 closer to parallel with the concrete surface 130. Alternatively, moving the height adjustment lever 165 such that the outer ring 162 is at a greater distance from the housing 141 and the thrust collar 115 will bring the rotatable blade assembly 102 closer to the rim 118 of the thrust collar 115, moving the blades 105 to a position that is less parallel to the concrete surface 130. The height adjustment assembly 160 may further comprise a stop, such as a physical obstruction or another suitable mechanism, that may restrict the rotation of the outer ring 162 such that the cams 163 may not move past the edge of the profiles 161.

FIGS. 3A and 3B are perspective views of the blade pitch adjustment system 100 of FIGS. 1 and 2, illustrating pitch adjustment of the blades 105. FIG. 3A shows the blades 105 in a position that is substantially parallel to the concrete surface 130. The cams 163 are substantially at the bottom of the profiles 161 and the outer ring 162 is relatively close to the housing 141. The rotatable blade assembly 102 is relatively far away from the thrust collar 115.

FIG. 3B shows the blade pitch adjustment system 100 where the blades 105 have been rotated to have a greater angle or pitch with respect to the concrete surface 130. The cams 163 are near the top of the profiles 161, the outer ring 162 being relatively far away from the housing 141. The rotatable blade assembly 102 is relatively close to the thrust collar 115.

When the blade pitch adjustment system 100 is set on a surface 130, such as a concrete surface, the surface 130 applies a force to the blade 105, which applies a rotational force to the rotatable blade arm 104 and lever 106. The lever 106 contacts the rim 118 which transfers the force to the common hub 110 and shaft 120. The force on the shaft 120 may cause the shaft 120 to slide down with respect to the gearbox 140, which may be opposed by the connected height adjustment assembly 160.

In use, power may be applied to the shaft 120, causing rotation. Rotation of the shaft 120 will rotate the rotatable blade assembly 102. As the rotatable blade assembly 102 rotates, frictional contact between each lever 106 and the rim 118 may rotate the outer collar 116 at substantially the same angular velocity as the rotatable blade assembly 102.

As best shown in FIG. 2, the height adjustment assembly 160, the shaft 120, the thrust collar 115, and the rotatable blade assembly 102 are configured to be substantially coaxial. Because these components are arranged substantially coaxially and are configured to remain substantially coaxial to a shared axis when moved, moving, and/or actuated, the rotatable blade assembly 102 may be moved up and down along the shared axis while remaining substantially perpendicular to the shared axis, and operatively parallel to the thrust collar 115. Because the thrust collar 115 is operatively parallel to the rotatable blade assembly 102, wear may be evenly distributed among wearable parts of the system.

As described previously, known blade pitch adjustment systems generally apply force in a non-coaxial manner, and thus may cause one or more of the components to move out of alignment with the other components, as made evident by uneven component wear and/or unpredictable movement and/or poor machine balance. By contrast, a machine that includes the blade pitch adjustment system 100 may advantageously distribute force evenly among the components, which may distribute wear substantially equally among the wearable components. Additionally, keeping the components substantially level may allow the whole machine to be more stable and to remain substantially level while being operated.

In other embodiments, the height adjustment assembly 160 may adjust the distance between the thrust collar 115, and the rotatable blade assembly 102. The height adjustment assembly 160 may not start and/or remain coaxial with the shaft 120, the thrust collar 115, and the rotatable blade assembly 102.

For example, rather than a plurality of cams, such as three cams, a height adjustment assembly 160 may comprise plurality of actuators, such as hydraulic rams or other suitable actuators, spaced non-coaxially to the shared axis and operatively connecting to the rotatable blade assembly 102, such as by contacting the outer ring 162. Contact points of the actuators operatively form a movable plane that may adjust the rotatable blade assembly 102 while keeping it coaxial to the shared axis and operatively parallel to the lower rim 118 of the thrust collar 115. The actuators may raise or lower the rotatable blade assembly 102 along the shared axis without changing the orientation of the shaft 120, the thrust collar 115, or the rotatable blade assembly 102 with respect to the shared axis. Alternatively, the thrust collar 115 may be similarly raised or lowered by the actuators, while remaining in its same orientation with respect to the shared axis.

In another embodiment, two or more pivoting levers, such as two conventional forks, with at least three combined contact points may be used to change the distance between the rotatable blade assembly 102 and the thrust collar 115. Contact points of the one or more pivoting levers form a moveable plane that may be positioned to contact the outer ring 162. The pivoting levers may be positioned on one or more sides of the shared axis without being concentric or coaxial with the shared axis. Further, if the pivoting levers are suitably controlled, the points of contact need not be coaxial to maintain the rotatable blade assembly 102 and the thrust collar 115 in an operatively parallel configuration. When actuated, the one or more pivoting levers may pivot, moving one or more components connected to the height adjustment assembly 160 without changing the orientation of the one or more components with respect to the shared axis. Alternatively, the thrust collar 115 may be raised or lowered by the pivoting levers, while remaining substantially perpendicular to the shared axis and operatively parallel to the rotatable blade assembly 102, to adjust the pitch of the blades.

FIG. 4 is a block diagram of another embodiment of a blade pitch adjustment system 400 of the present disclosure. The blade pitch adjustment system 400 comprises a height adjustment assembly 460, a thrust collar 415, and a rotatable blade assembly 402, which includes a plurality of levers 406, a plurality of rotatable blade arms 404, and a plurality of blades 405. The height adjustment assembly 460 is operatively connected to the rotatable blade assembly 402 and the rotatable blade assembly 402 persistently contacts the thrust collar 415.

The plurality of levers 406 are configured to persistently contact at least a portion of the thrust collar 415. Each blade 405 and each lever 406 is rigidly connected to one of the plurality of rotatable blade arms 404. When acted upon by a force, the lever 406 may rotate the connected rotatable blade arm 404 in the direction of the force, which may rotate the blade 405, changing the pitch of the blade 405.

The height adjustment assembly 460 is configured to change the distance between the rotatable blade assembly 402 and the thrust collar 415, such as by moving at least a portion of the assembly 402 toward or away from the thrust collar 415 while maintaining the relationship of the assembly 402 and the collar 415 to each other. For example, if the assembly 402 and the collar 415 are operatively parallel to each other, they will remain operatively parallel as the distance between them is adjusting and/or has been adjusted. When the distance between the rotatable blade assembly 402 and the thrust collar 415 is adjusted, the lever 406 will continue to contact the thrust collar 415, following the thrust collar 415, and rotating the arm 404, thus changing the pitch of the blade 405. This configuration may be best suited for use with a concrete finishing machine that comprises a single power unit that powers a plurality of rotatable blade assemblies 402.

The height adjustment assembly 460 may be configured to further connect to a user actuated adjustment mechanism, such as a lever, a tension cable, and/or a power assisted or power actuated adjustment mechanism. The height adjustment assembly 460 may be coaxial with an axis shared by the thrust collar 415 and the rotatable blade assembly 402. For example, the height adjustment assembly 460 may comprise a planar, annular ring that is configured to adjust the height of the rotatable blade assembly 460. Alternatively, one or more portions of the height adjustment assembly 460 may not be coaxial with the shared axis.

The rotatable blade assembly 402 may be configured to operatively connect to a power unit, such as an internal combustion power unit, a pneumatic power unit, a hydraulic power unit, an electric power unit, or another suitable power unit.

FIG. 5 is a block diagram of yet another embodiment of a blade pitch adjustment system 500 in accord with the current disclosure. The blade pitch adjustment system 500 comprises the same elements as the blade pitch adjustment system 400, but with an alternative configuration. In the embodiment of FIG. 5, the height adjustment assembly 560 is connected to the thrust collar 515, which is persistently contacted by the rotatable blade assembly 502. In this configuration, the height adjustment assembly 560 may move at least a portion of the thrust collar 515 with respect to the rotatable blade assembly 502 while still keeping the thrust collar 515 operatively parallel to the rotatable blade assembly 502. This configuration may be best suited for use with a concrete finishing machine that comprises a single power unit that powers a single rotatable blade assembly 502 or that comprises multiple power units that each power a single rotatable blade assembly 502.

FIG. 6 shows an embodiment of a ride-on concrete finishing machine 600 which comprises a rotatable blade assembly 102, a guard 605 connected to a frame 610, a body 615 connected to the frame 610, a seat 620 connected to the body 615, and may comprise a blade pitch adjustment system (not shown), such as the systems 100, 400, 500 previously described. Typically, the guard 605 is positioned close to the concrete surface 130 and may prevent damage when the ride-on concrete machine 600 contacts an obstacle, such as a pipe or wall. Generally, ride-on concrete finishing machines may comprise one or more rotatable blade assemblies 102, such as one, two, three or four, which may be connected to one or more blade pitch adjustment systems, as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure.

Typically, conventional blade pitch adjustment systems adjust the pitch of the blades 105 without adjusting the height of the rotatable blade assembly 102 with respect to the concrete surface 130. Because the blades 105 may raise the machine when pitched, the guard 605 may be disadvantageously raised, which may allow obstacles, such as pipes, to pass under the guard 605 causing damage to the blades 105 and/or the obstacle. By contrast, The blade pitch adjustment system 100 may be advantageous used with the concrete finishing machine 600 to adjust the pitch of the blades 105 while concurrently adjusting the distance between the frame 610 and the rotatable blade assembly 102. Moving the rotatable blade assembly 102 closer to the frame 610 allows the guard 605 to remain nearer the concrete surface 130, which may allow the guard 605 to continue to prevent damage from an obstacle when the blades 105 are at a large height or pitch.

Alternatively, the ride-on machine 600 may be configured with the blade pitch adjustment system, which may not adjust the height of the machine concurrently with adjusting the pitch of a plurality of blades 105, as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure.

FIG. 7 illustrates a known walk behind concrete finishing machine 700. A description of an embodiment of a walk-behind concrete finishing machine may be found in U.S. patent application Ser. No. 11/615,719 entitled “LINEAR LOST MOTION POSITIONING MECHANISM,” which is incorporated herein, in its entirety, by reference.

The walk-behind concrete finishing machine 700 comprises a guard 705, a frame 710, and a body 715. The walk-behind concrete finishing machine 700 may benefit from the use of a blade pitch adjustment system that is configured to adjust the rotatable blade assembly 102 with respect to a thrust collar while maintaining the assembly 102 and the collar in an operatively parallel relationship. The blade pitch adjustment system may comprise coaxial components, and may comprise components that are not coaxial. The blade pitch adjustment system may be similar to the blade pitch adjustment system 100 and may adjust the height of the machine 700 concurrently with adjusting the pitch of the blades 105. Alternatively, the machine 700 may be configured to use the blade pitch adjustment system, which may not adjust the height of the machine 700 concurrently with adjusting the pitch of the blades 105, as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure.

FIG. 8 illustrates an embodiment of a concurrent blade pitch adjustment actuation system 800 of the current disclosure. The system 800 comprises a linear actuator 810 connected to a frame member 830. The linear actuator 810 comprises a shaft 812 that is rotatably connected to a tension adjustment member 820 at an off-center connection point 816. As shown in FIG. 8, the frame member 830 further connects to a mounting member 835, such as a plate, that may further connect to a machine, such as, for example, a ride-on concrete finishing machine 600 (shown in FIG. 6). The tension adjustment member 820 may be rotatably connected to the frame member 830 at a connection point 822 that is approximately at the center of the tension adjustment member 820.

The tension adjustment member 820 has two arms, of about equal length, extending out from the center connection point 822 and is connected to a left tension cable 840 at a left side end 824 and to right tension cable 850 at a right side end 826. The tension adjustment member 820 may comprise greater than two ends 824, 826, enabling it to connect to greater than two tension cables 840, 850. As illustrated by FIG. 8, the tension cables 840, 850 are flexible to a degree and may be oriented to a new direction by one or more suitable mechanisms, such as by a left pulley 842 and/or by a right pulley 852. The left and right tension cables 840, 850 may each connect to a connector 844, 854, respectively, that may connect to a blade pitch adjustment system or mechanism, such as, for example, to a rotatable portion of a blade pitch adjustment system 846, 856. The tension cables 840, 850 may each be operatively connected to the rotatable portion 846, 856 through additional linkages or mechanisms (not shown).

Tension on the tension cables 840, 850 may be adjusted by rotating the tension adjustment member 820 about the connection point 822 with the linear actuator 810. For example, the shaft 812 of the linear actuator 810 may be extended, applying a force to one side of the tension adjustment member 820, and rotating the tension adjustment member 820 about the connection point 822. As illustrated in FIG. 8, rotation in first direction, by the tension adjustment member 820, will increase the tension on the tension cables 840, 850 concurrently and at the same rate. Further, the shaft 812 of the linear actuator 810 may be retracted, rotating the tension adjustment member 820 in a direction opposite the first direction, decreasing tension on the tension cables 840, 850 concurrently and at the same rate. In some embodiments, the concurrent blade pitch adjusting system 800 may be configured to have a different motion, such as with a clockwise or counter-clockwise rotational movement or with a linear movement, as would be apparent to one of ordinary skill in the art given the benefit of this disclosure.

The concurrent blade pitch adjustment actuation system 800 may be configured to concurrently adjust the pitch of trowel blades on a concrete finishing machine comprising multiple blade assemblies, each with an adjustable pitch. The concrete finishing machine may be, for example, the ride-on concrete finishing machine 600, or, in another example, a walk-behind concrete finishing machine with a plurality of adjustable pitch blade assemblies.

With respect to concrete finishing machines, a blade pitch adjustment mechanism may be a conventional fork and collar system, a coaxial ramp and collar system, or another suitable system, as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure.

Blade pitch adjustment mechanisms used by concrete finishing machines generally adjust the pitch of a plurality of blades by contacting and rotating a lever for each trowel blade of a blade assembly. For example, a plurality of levers may be contacted by a slidable collar that can move up and down with respect to the levers. Movement by the collar with respect to the levers will rotate the levers and connected trowels blades, changing the pitch of the blades to a smaller or larger pitch. Typically, a blade that is more parallel to a concrete surface is said to have a small pitch.

Because a concrete finishing machine is generally configured to have the trowel blades resting directly on a concrete surface, with the trowels holding the full weight of the machine, the blades are biased by gravity toward having a small or zero pitch. When a blade pitch adjustment mechanism is actuated to move the blades to a greater pitch, the pitch adjustment mechanism is overcoming the bias of the blades. For example, if the trowel blades are parallel to the concrete surface, the blade pitch adjustment mechanism may apply a force to the plurality of blades to rotate them to a greater pitch. Additionally, a force may be constantly applied to the blades to maintain the pitch of the blades, resisting the bias, and keeping them from rotating back to a smaller pitch. By contrast, to reduce the pitch of the blades, the force applied to the blade pitch adjustment mechanism may be reduced, allowing the bias to assert itself, moving the blades. When a desired pitch is achieved, the maintenance force may again be applied to the blades.

Referring again now to FIG. 8, the concurrent blade pitch adjustment actuation system 800 advantageously uses a single linear actuator 810 to change the tension of tension cables 840, 850. The linear actuator 810 may be a hydraulic cylinder, a pneumatic cylinder, an electric linear actuator, a mechanical linkage, or another suitable mechanism. A system 800 comprising a single linear actuator 810 that can actuate a plurality of blade pitch adjustment mechanisms may be less expensive to purchase and may require less maintenance than other conventional methods of actuation, which generally use one linear actuator per blade pitch adjustment mechanism. The cost advantage may be seen in the cost of the materials for the system 800, and/or in the cost of a control mechanism or circuit that may be connected to the system 800. Further, a system 800 using a single linear actuator 810 may not suffer from blade pitch matching problems, such as the problems discussed in the background section of this disclosure. For example, the linear actuator 810 may comprise a hydraulic cylinder that may leak fluid. Because a single linear actuator 810 is used, the fluid leak will affect both tension cables 840, 850 substantially equally and will not cause a mismatch in blade pitch between a plurality of connected blade assemblies.

Although the concurrent blade pitch adjustment actuation system 800 has been described regarding its use with blade pitch adjustment mechanisms that are commonly associated with concrete finishing machines it would be recognized by one of ordinary skill in the art, given the benefit of this disclosure, that the concurrent blade pitch adjustment actuation system 800 could be used with other suitable adjustable pitch blade adjustors and assemblies, such as with a plurality of fan blades.

As describe above, a plurality of blade pitch adjustment mechanisms can be actuated concurrently and at the same rate, which works well when a machine is suitably adjusted. However, the components of the concurrent blade pitch adjustment actuation system 800 and/or associated mechanisms may wear and/or shift over time, which may cause the pitch of one rotatable blade assembly to vary with respect to another rotatable blade assembly. It would be beneficial to provide a mechanism that can shift the pitch or adjust the bias of a plurality of rotatable blade assemblies with respect to each other.

As shown in FIG. 8, the linear actuator 810 is connected to the frame member 830 by a fastener 814, such as a bolt. The frame member 830 may be slidably connected to the mounting member 835, such as, for example, with a plurality of connectors 832, 834, which may project through one or more slots formed into the mounting member 835 (as shown in FIG. 9). The frame member 830, linear actuator 810, and tension adjustment member 820 may be adjusted or biased to provide substantially the same or a substantially different tension to the tension cables 840, 850. For example, by loosening the connectors 832, 834 and sliding the frame member 830, the tension on tension cables 840, 850 may be adjusted to be substantially the same. In another example, the tension on the tension cables 840, 850 may be biased to be greater on one tension cable.

Alternatively, the frame member 830, linear actuator 810, and tension adjustment member 820 may be adjusted or biased as a unit with a power adjuster, such as by an operatively connected second linear actuator 960 (shown in FIG. 9), as will be further discussed.

FIG. 9 illustrates a bias adjustment system 900. As shown in FIG. 9, the bias adjustment system 900 comprises a second linear actuator 960 connected to the mounting plate 835 at one end by a connector 962. The linear actuator 960 may be electric, pneumatic, hydraulic, mechanical, or another suitable power type and is operatively connected to the connector 822, which may be positioned such that a portion of the connector 822 passes through an aperture or slot formed in the frame member 830 and/or the mounting plate 835.

As illustrated by FIG. 9, the frame member 830, the connected linear actuator 810, and the tension adjustment member 820 may be slidably connected to the mounting member 835. The linear actuator 960 may be actuated such that it slides the frame member 830, linear actuator 810, and the tension adjustment member 820 to one side or the other. If the tension adjustment member 820 is moved from one side to another, the tension cables 840, 850 will move with the tension adjustment member 820, shifting tension from one tension cable to the other. The shift in tension may bias the pitch of a rotatable blade assembly such that it matches the pitch of another rotatable blade assembly. Alternatively, the position of the tension adjustment member 820 may be shifted such that the pitches of a plurality of rotatable blade assemblies are biased to be unequal.

The bias adjustment system 900 may be used with a ride-on style concrete finishing machine, such as the machine 600 (shown in FIG. 6), a walk-behind concrete finishing machine 700 (shown in FIG. 7), or with another suitable machine comprising a plurality of blade pitch adjustment mechanisms.

FIGS. 10 and 11 illustrate an embodiment of a partial ride-on concrete finishing machine 1000 comprising a concurrent blade pitch adjustment actuation system 800 and a bias adjustment system 900 (shown in FIGS. 8 and 9). The partial ride-on concrete finishing machine 1000 may be used with, for example, the concrete finishing machine illustrated in FIG. 6, or with another ride-on or walk-behind concrete finishing machine, as would be apparent to one of ordinary skill in the art, given the benefit of this disclosure.

FIGS. 10 and 11 show a perspective view and a partially exploded perspective view, respectively, of the partial ride-on concrete finishing machine 1000. A complete ride-on concrete finishing machine 1000 may comprise with a body portion and a seat, such as, for example, the body 615 and the seat 620, shown in FIG. 6. As shown in FIGS. 10 and 11, the blade pitch adjustment actuation system 800 and the bias adjustment system 900 may be located in the about center of the machine 600. The machine 600 may further comprise a power unit (not shown) that may be positioned above or below the blade pitch adjustment actuation system 800, in about the center of the machine 600.

FIG. 12A is a perspective view of another embodiment of a blade pitch adjustment actuation system and FIG. 12B is an exploded perspective view of the same embodiment. The concurrent blade pitch adjustment actuation system 1200 shown in FIGS. 12A and 12B acts to change the pitch of rotatable blades similarly to the embodiments described above, with an actuator 1210 that is connected to a right tension cable 1250 and a left tension cable 1240. When actuated by a user the actuator 1210 may extend or retract a shaft, increasing the tension on right and left tension cables 1250, 1240 at substantially the same time and at substantially the same rate.

Although this invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments that do not provide all of the features and advantages set forth herein, are also within the scope of this invention. Therefore, the scope of the present invention is defined only by reference to the appended claims and equivalents thereof. 

1. A blade pitch adjustment system comprising: a thrust collar; a rotatable blade assembly coaxial with and persistently contacting the thrust collar, the rotatable blade assembly being operatively parallel to the thrust collar, and comprising a plurality of blades that are configured to have an adjustable pitch; and a height adjustment assembly configured to be coaxial with the thrust collar and the rotatable blade assembly and configured to change a distance between the thrust collar and the rotatable blade assembly such that the thrust collar and the rotatable blade assembly remain operatively parallel to each other before, during, and after a change in distance, wherein changing the distance between the thrust collar and the rotatable blade assembly adjusts the pitch of the blades.
 2. The blade pitch adjustment system of claim 1, wherein the height adjustment assembly is operatively connected to the thrust collar and is configured to adjust the position of the thrust collar with respect to the rotatable blade assembly while keeping the thrust collar operatively parallel to the rotatable blade assembly.
 3. The blade pitch adjustment system of claim 1, wherein the height adjustment assembly is operatively connected to the rotatable blade assembly and is configured to adjust the position of the rotatable blade assembly up and down with respect to the thrust collar while keeping the rotatable blade assembly operatively parallel to the thrust collar.
 4. The blade pitch adjustment system of claim 1, further comprising power unit mated with a power transfer shaft, the power transfer being connected to the rotatable blade assembly.
 5. The blade pitch adjustment system of claim 1, wherein the rotatable blade assembly further comprises a hub connecting to a plurality of rotatable blade arms, each of the rotatable blade arms comprising at least one lever, wherein at least one of the plurality of blades is attached to each rotatable blade arm, and wherein the lever is configured to persistently contact at least a portion of the thrust collar.
 6. The blade pitch adjustment system of claim 1, wherein the height adjustment assembly comprises an outer ring, a profile follower, a bearing positioned coaxially with the outer ring, and a height adjustment collar, wherein the height adjustment collar comprises one or more height adjustment profiles, and wherein the profile follower is configured to contact and travel along the height adjustment profiles.
 7. The blade pitch adjustment system of claim 6, wherein the profile follower comprises a plurality of cams, a plurality of bearings, or a plurality of complementary ramps.
 8. A blade pitch adjustment system comprising: a thrust collar; a rotatable blade assembly operatively connected to and operatively parallel with the thrust collar, and comprising a plurality of blades that are configured to have an adjustable pitch; and a height adjustment assembly comprising at least three contact points, operatively forming a movable plane, and being configured to adjust a distance between the thrust collar and the rotatable blade assembly by adjusting the height of the at least three contact points, such that the thrust collar and the rotatable blade assembly remains operatively parallel to each other during and after distance adjustment, wherein adjusting the distance between the thrust collar and the rotatable blade assembly correspondingly adjusts the pitch of the blades.
 9. The blade pitch adjustment system of claim 8, wherein the at least three contact points operatively connect to the thrust collar and are configured to adjust the position of the thrust collar with respect to the rotatable blade assembly while keeping the thrust collar operatively parallel to the rotatable blade assembly.
 10. The blade pitch adjustment system of claim 8, wherein the at least three contact points operatively connect to the rotatable blade assembly and are configured to adjust the position of the rotatable blade assembly with respect to the thrust collar while keeping the rotatable blade assembly operatively parallel to the thrust collar.
 11. The blade pitch adjustment system of claim 8, wherein the rotatable blade assembly, the thrust collar, and the three contact points are coaxial.
 12. The blade pitch adjustment system of claim 8, wherein the height adjustment assembly comprises an outer ring, a bearing operatively connected to the outer ring and positioned coaxially within the outer ring.
 13. A concrete finishing machine comprising: a frame; a guard connected to the frame; a power unit connected to the frame; a rotatable blade assembly operatively connected to the power unit and comprising a plurality of blades that are configured to have an adjustable pitch and that are rotatably connected to a hub, the rotatable blade assembly being generally planar; a thrust collar having a planar rim and being configured to contact at least a portion of the rotatable blade assembly at the planar rim, the planar rim being operatively parallel to the plane of the rotatable blade assembly; and a height adjustment assembly configured to adjust a distance between the thrust collar and the rotatable blade assembly such that the planar rim of the thrust collar and the plane of the rotatable blade assembly remain operatively parallel to each other during and after distance adjustment.
 14. The concrete finishing machine of claim 13, further comprising an actuator configured to actuate the height adjustment assembly.
 15. The concrete finishing machine of claim 13, further comprising a plurality of rotatable blade assemblies, a plurality of height adjustment assemblies, and a plurality of thrust collars.
 16. The concrete finishing machine of claim 13, wherein the distance between the guard and the concrete surface is substantially the same, regardless of the pitch of the plurality of blades.
 17. The concrete finishing machine of claim 13, further comprising a power transfer shaft operatively connected to the power unit and operatively connecting the rotatable blade assembly to the height adjustment assembly.
 18. The concrete finishing machine of claim 13, further comprising a frame member operatively connected to the frame; a tension adjustment member connected to the frame member at a connecting point, the tension adjustment member having a plurality of ends; a plurality of tension cables operatively connected to the plurality of ends of the tension adjustment member; and a first actuator having a first end connected to the tension adjustment member and a second end connected to the frame member.
 19. The blade pitch adjustment system of claim 18, further comprising a mounting member connected to the frame, wherein the frame member is slidably connected to the mounting member.
 20. The blade pitch adjustment system of claim 19, further comprising a second actuator, a first end of the second actuator being connected to the mounting member, and a second end of the second actuator being operatively connected to the tension adjustment member. 